Backlight device, light source device, lens, electronic apparatus and light guide plate

ABSTRACT

Disclosed herein is a backlight device. The device includes: a light emitting element; a lens having an incident surface on which light emitted by the light emitting element is incident, and an outgoing surface which has an ability to converge the light and from which the light incident on the incident surface goes out; a light guide plate having a light incidence plane and introducing through the incidence plane the light going out from the outgoing surface, so as to perform surface light emission; and a reflective member operative to reflect a portion of the light going out from the outgoing surface of the lens, toward the incidence plane of the light guide plate.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit under 35U.S.C. §120 of U.S. patent application Ser. No. 13/606,766, titled“BACKLIGHT DEVICE, LIGHT SOURCE DEVICE, LENS, ELECTRONIC APPARATUS ANDLIGHT GUIDE PLATE,” filed on Sep. 7, 2012, which is a divisional of andclaims the benefit under 35 U.S.C. §120 of U.S. patent application Ser.No. 11/890,333, filed on Aug. 6, 2007, which claims the benefit under 35U.S.C. §119 of Japanese Patent Application JP 2006-216803, filed on Aug.9, 2006. The entire contents of these applications are herebyincorporated by reference in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a backlight device for generating lightin, for example, a display for displaying a picture according toluminance based on the transmittance of the light, a lens used in thebacklight device, a light source device, an electronic apparatus, and alight guide plate.

2. Description of Related Art

In recent years, as a backlight mounted in a liquid crystal display,backlights using LEDs (Light Emitting Diodes) as light source have beenproposed and embodied into products. In a high-color-gamut LEDbacklight, LEDs independent for R (red), G (green) and B (blue) colorsare used, whereby it has become possible to achieve color reproductionwith an NTSC (National Television System Committee) ratio of 100% ormore. Displays having such a LED backlight are now expected to becommercialized in the forms of PC (Personal Computer), amusement gears,or in-vehicle use.

In the case of backlights of intermediate sizes ranging from about 7 to17 inches, it is essential to reduce the thickness of the backlight.Here, in the so-called directly underlying type backlight, LEDs arearranged on the rear side of the display surface of a liquid crystalpanel and along the display surface. Most of large-sized backlightsinclude the directly underlying type backlight. However, in order torealize a thin type backlight as above-mentioned, it is indispensable todesign a backlight of the so-called edge light type (side edge type) inwhich light is emitted from an edge of a light guide plate. As anexample of the edge light type backlight, a technology of backlight witha contrivance for keeping the luminescent surface uniform has beendisclosed in Japanese Patent Laid-open No. Hei 11-212479 (hereinafterreferred to as Patent Document 1).

The invention pertaining to backlight in Patent Document 1 aims not at areduction in thickness but at eliminating irregularities in luminanceand contriving a reduced weight, even in a large-sized display (referto, for example, paragraphs [0016], [0017], etc., FIGS. 1 and 3 ofPatent Document 1). Specifically, as shown in FIG. 1 in Patent Document1, four light sources (3) are provided so as to secure a predeterminedluminance, and a clearance (11) is provided between light guide plates(9), (10) so as to contrive a reduced weight. In addition, as shown inFIG. 3 of Patent Document 1, cylindrical lenses (12) is disposed alongboth end parts of the clearance (11), whereby the light emitted from thelight sources (3) is converged, and is uniformly dispersed in the arearanging from end parts to central parts of the light guide plates (9),(10). Incidentally, the light sources (3) are composed of hot cathodetubes or cold cathode tubes, as described in paragraph [0002] of thespecification of Patent Document 1.

As a backlight using LEDs as light sources, a backlight reduced inluminance irregularities has been proposed (refer to, for example,Japanese Patent Laid-open No. 2005-196989 (hereinafter referred to asPatent Document 2)). In this backlight, the luminous intensitydistributions of the RGB LEDs are controlled to within predeterminedranges, whereby irregularities in color and in luminance are reduced(refer to, for example, paragraph [0058], FIG. 3 of Patent Document 2).

SUMMARY OF THE INVENTION

In the case of a structure in which LEDs are disposed substantially inclose contact with a light guide plate, as in the structure of the edgelight type backlight disclosed in Patent Document 2, irregularities inchromaticity or luminance such as the so-called bulb shape appearingphenomenon are largely generated especially at an incidence part of thelight guide plate even if the interval of the LEDs is small.

Thus, there is a need for a technology by which irregularities inluminance or chromaticity can be suppressed.

According to one embodiment of the present invention, there is provideda backlight device. The device includes: a light emitting element; alens having an incident surface on which light emitted by the lightemitting element is incident, and an outgoing surface which has anability to converge the light and from which the light incident on theincident surface goes out; and a light guide plate having a lightincidence plane and introducing through the incidence plane the lightgoing out from the outgoing surface, so as to perform surface lightemission. The device further includes a reflective member operative toreflect a portion of the light going out from the outgoing surface ofthe lens, toward the incidence plane of the light guide plate.

In the one embodiment of the present invention, the lens has theoutgoing surface having a light converging ability, so that the lightincident on the incident surface can be collected as much as possible,and the collected light can be made to go out toward the light guideplate. In addition, by the reflective member for reflecting the lightgoing out from the outgoing surface of the lens toward the incidenceplane of the light guide plate, the light going out from the outgoingsurface and not going directly toward the light guide plate can also beintroduced into the light guide plate. This makes it possible toincrease the amount of the rays of light introduced into the light guideplate, to achieve uniform surface light emission, and to suppressirregularities in luminance. Besides, the luminance itself can beenhanced.

In the backlight device as above, preferably, the outgoing surface has afirst principal surface (principal plane) having the converging ability,and a side surface provided at a side part of the first principalsurface; and the backlight device further includes a reflective partprovided so as to face the side surface and causing the light going outfrom the side surface to be again incident on the side surface and to goout through the first principal surface. The light going out from theside surface is light that would not be introduced into the light guideplate if the reflective part were absent. The presence of the reflectivepart ensures that the light going out from the side surface is furthermade to be incident on the lens and be utilized, whereby the amount ofthe rays of light introduced into the light guide plate is increased,and uniform light can be obtained. Besides, this makes it possible toenhance the light use efficiency and to enhance the luminance.

In the backlight device as above, preferably the outgoing surface has afirst principal surface having the converging ability, and a sidesurface provided at a side part of the first principal surface; and thereflective member has a first reflective surface operative to reflect aportion of the light going out from the outgoing surface of the lens,toward the incidence plane of the light guide plate, and a secondreflective surface provided so as to face the side surface andreflecting the light going out from the side surface to cause the lightto be again incident on the side surface and go out through the firstprincipal surface. The light going out from the side surface is lightthat would not be introduced into the light guide plate if the secondreflective surface were absent. The presence of the second reflectivesurface ensures that the light going out from the side surface isfurther made to be incident on the lens and be utilized, whereby theamount of the rays of light introduced into the light guide plate isincreased, and uniform light can be obtained. In addition, since thesingle reflective member has both the functions of the first and secondreflective surfaces, a reduction in the size or thickness of thebacklight device can be realized.

In the backlight device as above, preferably, the reflective memberincludes a base part having the second reflective surface, and a wedgepart having the first reflective surface and having a width whichgradually decreases in the thickness direction of the light guide plateas one goes from the base part toward the light guide plate. Thereflective member is used also as a member for positioning the lens.There is no need to separately provide a lens-fixing member or the like,so that a reduction in the size or thickness of the backlight device canbe realized, and the backlight device is simplified in structure.

In the backlight device as above, preferably, the incident surfaceincludes a second principal surface having a converging ability, and aprojected surface provided at an end part of the second principalsurface and projected from the second principal surface. This ensuresthat, for example, even when light diffused widely from the lightemitting element to the surroundings is generated, the light can beefficiently collected through the projected surface into the lens. Theconverging ability of the first principal surface and the convergingability of the second principal surface may be different or the same.

In the backlight device as above, preferably, the incident surface hasan ability to diverge the light. This ensures that, even when the lightis diverged at the incident surface, the light can be converged by thefirst principal surface, and the light going out from the side surfacecan be reflected by the reflective part and the second reflectivesurface, so that light use efficiency can be enhanced.

In the backlight device as above, preferably, the lens is a lens havinga cylindrical surface as the outgoing surface or the first principalsurface or a lens having a toroidal surface as the outgoing surface. Thesame applies also to the second principal surface.

In the backlight device as above, preferably, the lens has a reflectivesurface provided at a side part of the outgoing surface and reflectingthe light which is incident on the incident surface and which passesthrough the lens. While the light is reflected by the reflective part orthe second reflective surface in the above-mentioned configurations, thelens in this configuration has the reflective surface including thereflecting function.

In the backlight device as above, preferably, the light emitting elementis an element emitting the light in a plurality of colors. The lens isso configured that as much as possible of the rays of light emitted fromthe light emitting element at various angles can be taken in. Therefore,mixing of rays of light in a plurality of colors is promoted, and mixedcolor light free of irregularities in chromaticity or luminance can beproduced at the incidence plane of the light guide plate.

In the backlight device as above, preferably, the light guide plate hasa lens part or prism part provided at the incidence plane. Depending onthe shape of the outgoing surface of the lens, the dispersion of lightin the plane of the light guide plate may be comparatively small or maybe comparatively large. In this configuration, the magnitude of thedispersion of light can be controlled appropriately.

According to another embodiment of the present invention, there isprovided a backlight device. The device includes: a light emittingelement; and a lens having an incident surface on which light emitted bythe light emitting element is incident, an outgoing surface which has anability to converge the light and from which the light incident on theincident surface goes out, and a side surface provided at a side part ofthe outgoing surface. The device further includes a light guide platehaving a light incidence plane and introducing through the incidenceplane the light going out from the outgoing surface, so as to performsurface light emission; and a reflective part provided so as to face theside surface and causing the light going out from the side surface to beagain incident on the side surface and go out through the outgoingsurface.

According to this configuration, the light going out from the sidesurface of the lens is reflected by the reflective part, to be againintroduced through the side surface into the lens, whereby the amount ofrays of light introduced into the light guide plate is increased,uniform surface light emission can be obtained, and irregularities inluminance can be suppressed. In addition, light use efficiency isenhanced, and luminance itself can be enhanced.

Thus, according to the technologies of backlight and the like based onthe present invention, irregularities in luminance or chromaticity canbe suppressed. Besides, a reduction in cost and a simplified structurecan be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a backlight device according to anembodiment of the present invention;

FIG. 2 is a perspective view showing in an enlarged form a part of thebacklight device shown in FIG. 1;

FIG. 3 is a sectional view, taken along a horizontal plane, of a part ofthe backlight device;

FIG. 4 is a sectional view taken along line A-A of FIG. 3;

FIG. 5 shows a modification example of the order in which LEDs for RGBcolors are aligned in a light source block;

FIG. 6 shows design values of a lens;

FIG. 7 is a table showing design values specifying the shapes of firstand second principal surfaces of a lens;

FIG. 8 shows the manner in which rays of light generated from threelight source blocks, for example; are propagated through a lens and alight guide plate.

FIG. 9 shows the manner in which the rays of light in FIG. 8 aretransmitted, as viewed in an X-Z plane;

FIG. 10 is a sectional view showing a light source device according toanother example of the present invention;

FIG. 11 is a table showing design values specifying the shapes of aprincipal surface and an incident surface of a lens;

FIG. 12 shows the conditions of rays of light when three kinds of lightsource devices are operated to emit light;

FIG. 13 shows diagrams representing the luminous intensity distributioncharacteristics in the vicinity of incidence planes of light guideplates, in the three kinds of light source devices;

FIG. 14 shows the conditions of luminance and chromaticity in the lightguide plates, in the three kinds of light source devices;

FIGS. 15A to 15H show various modification examples of the lens;

FIGS. 16A to 16E show various modification examples of the light guideplate, showing the examples which differ in the cut pattern of theincidence plane; and

FIG. 17 is a partial sectional view showing a part of a laptop-type PCequipped with a display using the backlight device according to theabove embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, an embodiment of the present invention will be described below,referring to the drawings.

FIG. 1 is a perspective view showing a backlight device according to anembodiment of the present invention. FIG. 2 is a perspective viewshowing in an enlarged form a part of the backlight device 10 shown inFIG. 1. FIG. 3 is a plan view showing a part of the backlight device 10.The backlight device 10 is a device which is disposed mainly on the backside of a liquid crystal panel (not shown) having, for example, liquidcrystal elements as elements for modulating the transmittance of light.The backlight device 10 includes a light source device 1, a light guideplate 2, and optical sheets 3, 4. FIG. 3 is a sectional view, takenalong a horizontal plane, of a part of the backlight device 10, and FIG.4 is a sectional view taken alone line A-A of FIG. 3.

As shown in FIG. 1, the light source device 1 has, for example, aplurality of light source blocks 5, a lens 6 for leading the lightgenerated by the light source blocks 5 to the light guide plate 2, and areflective member 7 reflecting the light led from the lens 6. The lightsource block 5 includes, for example, LEDs 8 as light emitting elements.As shown in FIG. 4, in the light source block 5 in this embodiment, LEDchips for three primary colors of red (R), green (G) and blue (B) aremounted, and the LEDs 8 are potted with a transparent resin 9. It isideal for the transparent resin 9 to have a light transmittance of 100%,but, naturally, some absorption of light occurs in the transparent resin9 although it is “transparent”. As shown in FIG. 3, the light sourceblocks 5 are aligned in one row along an incidence plane 2 a of thelight guide plate 2 so that, in each of the light source blocks 5, theLEDs 8 are aligned in the color order of R, G and B from the left sidein the figure. However, as shown in FIG. 5, the light source blocks 5may be alternately reversely arranged in the arranging direction (Ydirection) so that the LEDs 8 are arranged in the color orders of RGB,BGR, RGB, . . . . Or, the light source blocks 5 may be arranged so thatthe color orders are directed at random.

The form of the light source block 5 is not limited to theabove-mentioned. For example, an LED for one color may be mounted ineach light source block, or LEDs for two colors may be mounted in eachlight source block. Or, one light source block may include LEDs for fouror more different colors or for substantially the same color. The colorsof the LEDs are not limited to the three colors of R, G and B; forexample, adoption of various colors such as yellow, orange and emeraldmay be contemplated. In other words, the color produced by the backlightdevice 10 (the color in which the light guide plate 2 performs surfacelight emission) is not limited to white but may be any of theabove-mentioned colors used singly (monochromic) or in combinationthereof. Or, a light source block including white-color LEDs may be usedas the light source block. In the case where each light source blockincludes LEDs for one color, light source blocks respectively for R, Gand B colors may be arranged in an order, or they may be arranged sothat the R, G and B colors may be arranged at random. The number of thelight source block(s) is not limited, and the number may be one or more.Where the number of the light source block(s) is one or a small number,power LEDs are desirably used. The number of the light source block(s)depends also on the size of the liquid crystal panel.

The light guide plate 2 and the optical sheets 3, 4 may be any ofvarious known ones. Examples of the optical sheet 3 disposed on the sideof the front surface 2 b of the light guide plate 2 (on the side onwhich the liquid crystal panel is disposed) include a prism sheet and adiffuser sheet. Examples of the optical sheet 4 disposed on the side ofthe rear surface 2 c of the light guide plate 2 include a reflectivesheet. In addition, a polarizing sheet may be included in the opticalsheets 3, 4. The prism sheet may be a normal prism sheet or a reverseprism sheet. However, the configurations and layout of the opticalsheets are not limited to the above-mentioned configurations and layout,and various known ones may be used, as above-mentioned.

The lens 6 is disposed oppositely to the incidence plane 2 a of thelight guide plate 2 so that it extends along the incidence plane 2 a,and is elongate in shape (see FIG. 3). The lens 6 is clamped between tworeflective members 7 in the thickness direction of the light guide plate2 (Z direction), for example. The reflective member 7 is formed to beelongate in the Y direction, and may be split in the Y direction intotwo or more parts. The lens 6 also may be a single elongate one or maybe split in the Y direction into two or more parts, like the reflectivemember 7.

As shown in FIG. 4, the reflective member 7 has a base part 7 a and awedge part 7 b, and the light source blocks 5 and the lens 6 are incontact with the base part 7 a. The wedge part 7 b has a tapered shapesuch that the thickness thereof gradually decreases as one goes awayfrom the base part 7 a. The wedge part 7 b has a first reflectivesurface 17 for reflecting a portion of the light going out from theoutgoing surface 6 a of the lens 6 toward the light guide plate 2. Theangle (for example, the angle against the optical axis, i.e., the Xaxis) of the first reflective surface 17 can be appropriately set. Onthe other hand, the base part 7 a has a second reflective surface 27which faces a side surface 36 of the lens 6 and which reflects the lightgoing out from the side surface 36 and causes the light to be againincident on the side surface 36. The light thus again incident on theside surface 36 goes out through the outgoing surface 6 a of the lens 6to be incident on the incidence plane 2 a of the light guide plate 2, aswill be described later. The first reflective surface 17 or the secondreflective surface 27 is realized by forming a film with a high lightreflectance by, for example, vapor deposition, sputtering, coating orthe like method. Or, alternatively, the material itself of thereflective member 7 may be a material having such a high reflectance.

The light source device 1 and the light guide plate 2 and the like arefixed by being positioned by appropriate members such as frames (notshown). The light source blocks 5, the lens 6 and the reflective members7 may be relatively positioned and fixed by use of adhesive materials orthe like fixing method, or they may not necessarily be in direct contactwith each other but may be fixed by appropriate fixing methods.

As shown in FIG. 4, the lens 6 has the incident surface 6 b on which thelight emitted from the light source blocks 5 is incident, and theoutgoing surface 6 a through which the light goes out. The outgoingsurface 6 a has a first principal surface 16 which has an ability toconverge the light, i.e., which is convex, and the side surfaces 36provided at side parts of the first principal surface 16. As has beenmentioned above, the side surface 36 of the lens 6 faces, and makescontact with, the second reflective surface 27 of the base part 7 a ofthe reflective member 7. The incident surface 6 b has a second principalsurface 26 having an ability to converge the light, and projectedsurfaces 46 provided at upper and lower end parts of the secondprincipal surface 26 and projected from the second principal surface 26.The projected surfaces 46 are each so provided as to form an optimumangle with a package surface 11 of the light source blocks 5. Theoptimum angle is, for example, such an angle as to ensure that as muchas possible of the light coming from the light source blocks 5 can bemade incident on the lens 6.

The first principal surface 16 is, for example, a toroidal surface or acylindrical surface. The second principal surface 26, also, is atoroidal surface or a cylindrical surface. The combination of the firstand second principal surfaces 16 and 26 may be the first principalsurface 16 being a toroidal surface with the second principal surface 26being a cylindrical surface, or may be the first principal surface 16being a cylindrical surface with the second principal surface 26 being atoroidal surface. Or, both the principal surfaces 16 and 26 may betoroidal surfaces, or may be cylindrical surfaces. The side surfaces 36are not limited to flat surfaces but may be curved surfaces. Like theside surfaces 36, the projected surfaces 46 may be curved surfaces.

Non-limitative examples of the material of the lens 6 includepolycarbonates, olefin resins, and glass materials. Each of thesematerials ensures heat resistance.

FIG. 6 shows design values of the lens 6. As shown in FIG. 6, the heighth1 of the lens 6, the thickness a1 of the lens 6, and the thickness b1of the lens 6 on the optical axis are, for example, so set that h1=2.94mm, a1=2.23 mm, and b1=2.10 mm. The length of the lens 6 in thelongitudinal direction, i.e., the direction orthogonal to the papersurface, namely, the Y direction in FIG. 5, is 43.34 mm. The LED chip inthe light source block 5 is about 0.3 mm square. These values are givenmerely as examples, and they can be appropriately modified.

FIG. 7 is a table showing design values specifying the shapes of thefirst and second principal surfaces 16 and 26 of the lens 6. In thisexample, both of the first and second principal surfaces 16 and 26 areaspheric surfaces (non-cylindrical surfaces), for example, toroidalsurfaces. In a rectangular coordinate system with the vertex of each ofthe principal surfaces 16 and 26 as an origin and with the optical axisdirection as X axis, let the curvature at the vertex of each principalsurface be c, the conic constant be k, and the 4th, 6th and 8th degreeaspheric coefficients be α2, α3 and α4, then the aspheric surfacedeformation amount ΔH(h), i.e., the aspheric surface, can be expressedby the following formula (1). In consideration of this rectangularcoordinate system, the height direction in the Z direction in the figurefrom the optical axis is taken as y axis.ΔH(h)=(cy ²/[1+{1−(1+k)c ² y ²}^(1/2)])+α2y ⁴+α3y ⁶+α4y ⁸  (1)

Now, referring to FIG. 4, the operation of the backlight device 10 willbe described.

Of the rays of light generated from each LED 8, those within apredetermined angular range are transmitted through the transparentresin 9, due to the influences of critical angles with respect to thepackage surface 11 and the second principal surface 26. As viewed in theX-Y plane with the X axis direction taken as an angle of 0 degree, therays of light transmitted through the transparent resin 9 are basicallydispersed substantially to 90 degrees. The lens 6 in this embodiment canlead also the rays of light with such a dispersion, to the light guideplate 2.

Of the rays of light transmitted through the transparent resin 9, thoserays at comparatively small angles to the optical axis of the lens 6(the X axis direction) are incident on the second principal surface 26.The rays of light incident on the second principal surface 26 arerefracted, pass through the lens 6, go out through the first principalsurface 16, and are introduced into the incidence plane 2 a of the lightguide plate 2. On the other hand, of the rays of light transmittedthrough the transparent resin 9, those rays at comparatively largeangles to the optical axis are incident on the projected surfaces 46.The rays of light incident on the projected surfaces 46 are refracted,go out through the side surfaces 36 of the lens 6, are then reflected bythe second reflective surfaces 27 of the reflective members 7, and areagain incident on the side surfaces 36 of the lens 6. The rays of lightincident on the side surface 36 go out through the first principalsurface 16, are then reflected by the first reflective surfaces 17 ofthe reflective members 7, and are introduced into the incidence plane 2a of the light guide plate 2 a.

FIG. 8 shows the manner in which the rays of light emitted from thethree light source blocks 5, for example, are propagated through thelens 6 and the light guide plate 2. FIG. 9 shows the same, as viewed inthe X-Z plane. It is seen from FIG. 8 that the rays of light aredispersed in the lens 6 in also the Y direction, i.e., in thelongitudinal direction of the lens 6. Thus, propagation of light in thelens 6 occurs not only in the optical axis direction but also crosswisedirection and skew directions, attended by multiple reflection occurringrepeatedly, whereby mixing of RGB colors of light emitted by the lightsource blocks 5 is promoted, and a desired white color can be produced.Of the light propagated through the lens 6 while undergoing multiplereflection repeatedly, about 65% is led to the light guide plate 2.

Thus, according to the light source device 1 in this embodiment, thelens 6 has the first principal surface 16 having a converging ability,so that it is possible to collect as much as possible the light incidenton the incident surface 6 b and to cause the collected light to go outtoward the light guide plate 2. In addition, the rays of light going outfrom the first principal surface 16 and not going directly to the lightguide plate 2 can also be introduced into the light guide plate 2, bythe first reflective surfaces 17 of the reflective members 7. Thisensures that the amount of the rays of light introduced into the lightguide plate 2 can be increased, a uniform surface light emission can beobtained, and irregularities in luminance can be suppressed. Besides,the luminance itself can be enhanced.

According to the lens 6 in this embodiment, the mixing of the RGB colorsof light emitted by the light source blocks 5 is promoted asabove-mentioned, so that a white color free of irregularities inchromaticity or in luminance can be produced at the incidence plane 2 aof the light guide plate 2.

The rays of light going out from the side surfaces 36 of the lens 6would not be introduced into the light guide plate 2 if the secondreflective surfaces 27 of the reflective members 7 were absent. But,actually, the second reflective surfaces 27 are present, whereby therays of light going out from the side surfaces 36 are made to be againincident on the lens 6 and be utilized; as a result, the amount of therays of light introduced into the light guide plate 2 is increased,whereby uniform light can be obtained. Besides, this leads to furtherpromotion of mixing of colors, whereby the above-mentioned effect isrealized.

Furthermore, since each of the reflective members 7 has both thefunctions of the first and second reflective surfaces 17 and 27, areduction in the size or thickness of the backlight device 10 can berealized. In addition, the reflective member 7 has also the function asa member for positioning the light source blocks 5 and the lens 6.Therefore, it is unnecessary to separately prepare a member or membersfor fixing the light source blocks 5 and the lens 6, which also makes itpossible to realize a reduction in the size or thickness of thebacklight device 10.

According to the lens 6 in this embodiment, since the projected surfaces46 are provided, even when rays of light dispersed widely from the lightsource blocks 5 to the surroundings are generated, the rays of light canbe efficiently collected into the lens 6 through the projected surfaces46.

Meanwhile, in general, the number of LED chips mounted varies dependingon whether a power-type LED is used or an ordinary LED is used, as theLED for constituting the backlight, in consideration of the quantity oflight emitted. The power-type LED is driven, for example, by about 10times the current value (about several hundreds of milliamperes) for theordinary LED. In the case of using the power-type LED, it is difficultto put the RGB chips adjacent to each other, taking into account thenumber of LEDs mounted and the measure for coping with heat. Therefore,the chip interval becomes large, which is disadvantageous in obtainingwhite light by mixing the RGB rays of light in a limited space. In thecase of using the power-type LED, few problems are generated if asufficient optical path can be secured, but it is very difficult toobtain a sufficient optical path, due to the problem as to the space forthe frame of the backlight and due to limitations in thickness attendanton a reduction in thickness of the system. In view of this, in somecases of the related-art backlight, conversion to white light is carriedout positively by utilizing a dichroic mirror; even in these cases,however, the size of the optical system yet causes some problems as toreductions in thickness and frame width.

On the other hand, utilization of the ordinary low-power LED makes itpossible to realize an extremely small intervals between the RGB LEDchips, which is advantageous in realizing reductions in thickness andframe (architrave) width. However, as has been mentioned above, in thecase of a structure in which LEDs are disposed substantially in closecontact with a light guide plate, as in the edge light type backlightstructure described in Patent Document 2, irregularities in luminanceand/or chromaticity would be generated even if the chip interval issmall.

Besides, in the case of the ordinary LED, utilization of the dichroicmirror is attended by the need to make the mirror itself thinner, whichbrings about a problem on a strength basis. In addition, since theoptical component parts are minute in size, a large rise in cost wouldresult from a rise in the cost of forming the reflective film and thelike. In the case of utilizing a dichroic mirror, a lens is insertedimmediately behind the LEDs so that the rays of light from the lightsource are once made parallel, and this configuration also is attendedby limitation to realizing a lower aperture ratio. The light sourcedevice 1 in this embodiment can solve these problems, and its simplestructure enables a reduction in cost and a reduction in size orthickness. In addition, the realization of the simple structure makes itpossible to reduce the width w (shown, for example, in FIG. 17) of theframe (architrave) supporting the light source device 1.

FIG. 10 is a sectional view showing a light source device according toanother embodiment of the present invention. Hereinafter, for the samemembers and functions or the like as those of the backlight device 10according to the embodiment shown in FIGS. 1 to 4 and the like, thedescriptions will be simplified or omitted, and the followingdescription will be centered on the differences from the above-describedembodiment.

In a light source device 51 shown in FIG. 10, the shape of the lens 12is different from that of the lens 6 in the light source device 1 shownin FIG. 4. Like the lens 6, the lens 12 faces the incidence plane 2 a ofthe light guide plate 2, and is elongate in the Y axis direction alongthe incidence plane 2 a. The lens 12 includes an incident surface 12 b,and an outgoing surface 12 a having a principal surface 22 and sidesurfaces 32 provided at side parts of the principal surface 22. Theheight h2 of the lens 12 and the thickness a2 of the lens 12 on theoptical axis are set to be h2=2.94 mm and a2=2.23 mm. The length in thelongitudinal direction, or the Y direction, of the lens 12 is 43.34 mm.These values may be modified appropriately.

FIG. 11 is a table showing design values for specifying the shapes ofthe principal surface 22 and the incident surface 12 b of the lens 12.The shape of the principal surface 22 is specified by the above formula(1); in this example, the principal surface 22 is a toroidal surface,and the incident surface 12 b is a flat (plain) surface. The lens 12 ispositioned relative to light source blocks 5 and reflective members 7 sothat side surfaces 32 constituting parts of the outgoing surface 12 a ofthe lens 12 face second reflective surfaces 27 of the reflective members7 and that the incident surface 12 b of the lens 12 faces a packagesurface 11 for the light source blocks 5.

With this configuration of the light source device 51, also, it ispossible to efficiently collect the rays of light emitted from the lightsource blocks 5 and to suppress the irregularities in chromaticity andluminance in the light guide plate 2.

FIG. 12 shows the conditions of rays of light emitted from three kindsof light source devices. The cases of a light source device withreflective members 7 and without any lens, the light source device 51shown in FIG. 10, and the light source device 1 shown in FIG. 4 areshown, in this order from the left side in FIG. 12. The upper diagramscorrespond to the cases of 50 rays of light, while the lower diagramscorrespond to the cases of 300 rays of light. Particularly in the lightsource device 51 and the light source device 1, the numbers of the raysof light in the lenses 12 and 6 are large, which indicates that mixingof colors is promoted.

FIG. 13 shows the luminous intensity distribution characteristics in thevicinity of the incidence plane 2 a of the light guide plate 2, in eachof the above-mentioned three kinds of light source devices. The cases ofthe light source with only the reflective members and without any lens,the light source device 51 shown in FIG. 10, and the light source device1 shown in FIG. 4 are shown, in this order from the upper side in FIG.13. The incident luminous fluxes (unit: lumen (lm)) are 265.7, 255.1,and 233.8, respectively. In the graphs of the luminous intensitydistribution characteristics, the solid line shows the condition asviewed in the X-Y plane in FIG. 4 or 10 (hereinafter referred to as“luminous intensity distribution in plane”). In this case, the radialdirection of the circle represents the luminous intensity (quantity oflight) (unit: candela (cd)), the vertical direction (angle: 0 degree)from the center of the circle is the optical axis direction (X axisdirection), and the left-right direction (±90 degrees) is thelongitudinal direction (Y axis direction) of the lens. Besides, thebroken line shows the condition as viewed in the X-Z plane in FIG. 4 or10 (hereinafter referred to as “luminous intensity distribution invertical plane”). In this case, the direction of angle of 0 degree isthe optical axis direction (X axis direction), and the direction of ±90degrees is the vertical direction (Z axis direction).

In the light source device without any lens, the absence of lens ensuresthat the quantity of light introduced into the light guide plate 2 islarge, and the light use efficiency is high. As for the luminousintensity distribution in plane, however, in the angular range of from−45 degrees to +45 degrees, strong peaks remain in the vicinity of ±27degrees. Besides, in the luminous intensity distribution in plane, thelight is largely split into the left and right parts, due to the layoutof the RGB LEDs 8 in the light source block 5. For example, the light onthe minus side is due mainly to the green LED, and the light on the plusside is due mainly to the blue LED. In addition, the light in thevicinity of 0 degree is due mainly to the red LED. As for the luminousintensity distribution in vertical plane, also, an angular dispersionexists. As the angle of the luminous intensity distribution in verticalplane is smaller, it is more favorable, and the light is led more nearlyperpendicularly to the incidence plane 2 a of the light guide plate 2.Thus, in the light source device without any lens, irregularities inchromaticity and luminance are generated at the incidence plane 2 a ofthe light guide plate 2.

In the light source device 51, the quantity of light is reduced by about4%, as compared with that in the light source device without any lens.However, the effect on mixing of RGB colors is favorable. As for theluminous intensity distribution in plane, the distribution is favorablethough there are some minute peaks in the angular range of from −45degrees to +45 degrees. As for the luminous intensity distribution insection, also, the distribution is favorable with a small angle ofdispersion.

In the light source device 1, the quantity of light is reduced by about12%, as compared with that in the light source device without any lens.However, the effect on mixing of RGB colors is the highest. As for theluminous intensity distribution in plane, there is no steep peak in theangular range of from −45 degrees to +45 degrees. As for the luminousintensity distribution in section, also, the distribution is favorablewith a small angle of dispersion.

FIG. 14 shows the conditions of luminance distribution and chromaticitydistribution in the light guide plate 2, in each of the above-mentionedthree kinds of light source devices. The cases of the light sourcedevice with only reflective members and without any lens, the lightsource device 51 shown in FIG. 10, and the light source device 1 shownin FIG. 4 are shown, in this order from the left side in FIG. 14. As forluminance in the light guide plate 2 in the light source device withoutany lens, the portion where the color is lighter on the upper side (thevicinity of the incidence plane 2 a in the light guide plate 2)indicates condensation of light, showing the generation ofirregularities in luminance. In this point, luminance irregularities aresuppressed in the light source device 51 and the light source device 1.

On the other hand, as for the chromaticity diagram, for each of thelight source devices, the left side represents the y-axis (irregularitygenerated in the range of from blue to green), and the right siderepresents the x-axis (irregularity generated in the range of from blueto red). Though it is difficult to confirm by the monochromic diagramsin FIG. 14, the light source device without any lens produced heavierirregularities in chromaticity, as compared with the other light sourcedevices 1 and 51.

FIGS. 15A to 15H show various modification examples of lens. The lensesshown in FIGS. 15E, 15F, 15G and 15H are lenses which have a divergingability at the light incident surfaces thereof, i.e., lenses which haveconcave incident surfaces. The conditions of rise-up of the luminousflux from the light guide plate 2 differ depending on the thickness,shape or system of the light guide plate 2, and, therefore, the shape oflens is also required to be changed as shown in FIGS. 15A to 15H.Incidentally, the meanings of the symbols in the figures are as follows:

-   f: flat surface-   c1: convex cylindrical surface-   c2: concave cylindrical surface-   t1: convex toroidal surface-   t2: concave toroidal surface.

FIGS. 16A to 16E show various modification examples of the light guideplate. While the incidence plane 2 a was a flat surface in theabove-described embodiments, different cut patterns of the incidenceplane are shown here. The incidence plane of the light guide plate shownin FIG. 16A has prism parts p; the incidence plane shown in FIG. 16B hasconvex prism parts p1; the incidence plane shown in FIG. 16C has convexprism parts p2; the incidence plane shown in FIG. 16D has convexcylindrical lens parts e1; and the incidence plane shown in FIG. 16E hasconcave cylindrical lens parts e2. In the case of a lens part composedof the convex cylindrical lens parts e1, light can be condensed in thelight guide plate. In the case of the convex cylindrical lens parts e2,light can be diverged in the light guide plate. In addition, thecylindrical surface may be replaced by a toroidal surface or otheraspheric surface.

In the respective incidence planes shown in FIGS. 16A to 16E, the pitchof the prisms or lenses may be fixed, varied, or set at random. Or, inthe incidence planes shown in FIGS. 16A to 16E, the height (the heightin the X axis direction) of the prisms or lenses may be fixed, varied,or set at random.

Besides, in the cases shown in FIGS. 16D and 16E, if the power at thelens part is insufficient, the incidence plane may be so formed as tohave a curvature as viewed in the X-Z plane, though not shown. The shapeof the curved surface in that case may be a cylindrical surface, atoroidal surface or other aspheric surface.

In the case of an incidence plane composed of a flat surface, if therefracting power at the incidence plane is insufficient, the use of anyof the light guide plates shown in FIGS. 16A to 16E increases therefracting power, which is very effective.

FIG. 17 is a partial sectional view showing a part of a laptop type PCin which a display using the backlight device 10 according to theabove-described embodiment is mounted. The PC 100 includes a main body55, and a display 45. The display 45 has a liquid crystal panel 44, andthe light source device 1 according to one of the above-describedembodiments and the like are disposed at a lower edge part 41. The lightsource device 1 may be disposed also at an upper edge part 42 inaddition to the lower edge part 41, or may be disposed only at the upperedge part 42. Or, the light source devices 1 may be disposed at left andright edge parts.

The scope of the present invention is not to be construed as limited tothe above-described embodiments, and the invention can be carried out inother various embodiments.

For example, while the liquid crystal panel has been mentioned as anexample of the element for modulating the transmittance of light, anymicro element operated, for example, an electrostatic action, apiezoelectric action, a magnetic action or the like may be adopted asthe element for modulating the transmittance of light.

The first reflective surface 17 or the second reflective surface 27 ofthe reflective member 7 may be a curves surface, instead of the flatsurface. Examples of the shape of the curved surface include variousshapes. In the reflective member 7, the second reflective surface 27 hasbeen described to be provided at the base part 7 a. However, the secondreflective surface 27 may be formed at each side surface 36 of the lens6. In that case, a film with a high light reflectance may be formed onthe side surface 36 by vapor deposition, sputtering, coating, or thelike method; alternatively, a reflective sheet (not shown) or the likemay be adhered to the side surface 36.

In the above description, the reflective member 7 has had a structureincluding the base part 7 a and the wedge part 7 b. However, thereflective member 7 may be provided with the base part 7 a and the wedgepart 7 b as separate members. In addition, in the above description, thereflective member 7 has had a structure in which the width of the wedgepart 7 b gradually decreases as one goes away from the base part 7 a.However, the reflective member 7 may simply have a substantiallyconstant thickness, instead of having the wedge-like shape.

As the backlight device 10 in the above-described embodiment, there maybe adopted a backlight device which, for example, does not have thelight guide plate 2 and in which the light going out from the lens 6 isreleased into air.

In the structure of the light guide plate 2, for example, the principalsurfaces (the surfaces to which the optical sheets 3, 4 are applied) ofthe light guide plate 2 may be in a prism-like shape. Or, the thicknessof the light guide plate 2 gradually increases as one goes away from thelight source device 1, i.e., the light guide plate 2 may have awedge-like shape. This makes it possible to further suppressirregularities in luminance and chromaticity.

While the PC 100 has been mentioned as an example of the electronicapparatus shown in FIG. 17, the present invention is applicable to TVand other various kinds of displays.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factor in so far as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. An apparatus comprising: a lens including anincident surface configured to receive light emitted by a light emittingelement; a side surface including a portion arranged to extend parallelto a base part of a reflective member; and an outgoing surfaceconfigured to converge light so that a portion of light incident on theincident surface is transmitted toward a wedge part of the reflectivemember; and the reflective member including the base part having aconstant thickness; and the wedge part integrally formed with the basepart, the wedge part extending from the base part and being tapered awayfrom the outgoing surface of the lens beginning at a junction of theside surface and the outgoing surface of the lens.
 2. The apparatus ofclaim 1, wherein the incident surface includes a principal surfaceconfigured to converge light and a projected surface provided at an endportion of the principal surface and projected from the principalsurface.
 3. The apparatus of claim 2, wherein the principal surface isone of a cylindrical surface and a toroidal surface.
 4. The apparatus ofclaim 1, wherein the outgoing surface has a principal surface configuredto converge light and the side surface provided at a side portion of theprincipal surface.
 5. The apparatus of claim 1, wherein the incidentsurface diverges light upon transmittal of light through the incidentsurface.
 6. The apparatus of claim 1, wherein the outgoing surface isone of a cylindrical surface and a toroidal surface.
 7. The apparatus ofclaim 1, wherein the portion of the side surface includes a flatsurface.
 8. The apparatus of claim 1, wherein the portion of the sidesurface includes a curved surface.
 9. The apparatus of claim 1, whereinthe wedge part is tapered from the base part.
 10. The apparatus of claim1, wherein the base part of the reflective member includes acomplementary portion that extends parallel to and is in alignment withthe portion of the side surface.
 11. The apparatus of claim 1, whereinthe incident surface is configured to transmit the portion of lightincident on the incident surface toward the base part of the reflectivemember through the side surface.
 12. The apparatus of claim 11, whereinthe base part of the reflective member is configured to reflect thelight received from the side surface toward the outgoing surface throughthe side surface.
 13. The apparatus of claim 1, wherein the outgoingsurface is configured to transmit the light received through the sidesurface toward the wedge part of the reflective member.
 14. Theapparatus of claim 13, wherein the wedge part of the reflective memberis configured to reflect the light received through the outgoing surfacetoward the incidence plane of the light guide plate.
 15. An apparatuscomprising: a lens including an incident surface configured to receivelight emitted by a light emitting element; a side surface; and anoutgoing surface; and a reflective member including a base part arrangedhaving a constant thickness and arranged to extend parallel to the sidesurface of the lens; and a wedge part integrally formed with the basepart, the wedge part having a progressively decreasing thickness as itextends away from the base part and configured to reflect light emittedfrom the outgoing surface of the lens.
 16. An apparatus comprising: areflective member including the base part having a constant thickness;and a wedge part integrally formed with the base part, the wedge partextending from the base part and having a progressively decreasingthickness as it extends away from the base part; and a lens including anincident surface configured to receive light emitted by a light emittingelement; a side surface including a portion arranged to extend parallelto the base part of the reflective member; and an outgoing surfaceconfigured to emit at least a portion of light incident on the incidentsurface toward the wedge part of the reflective member.